The 2015 Paris attackers were “on the radar” of French authorities, as were the Charlie Hebdo killers. The Copenhagen terrorists were known to local authorities. Man Haron Monis, who staged an attack in Sydney, had written a letter to Australia’s attorney general inquiring about whether he’d get into legal trouble for communicating with ISIS. The men behind the Quebec car-ramming and the shooting at parliament were known to Canadian authorities. Mehdi Nemmouche, who murdered four peoples at the Jewish Museum in Brussels, was a convicted armed robber who was under surveillance after traveling back and forth to Syria.

In that, terrorism is a lot like ordinary crime. Almost all of the murderers in New York City have prior criminal records, and New York is not unusual in this regard. A great deal of violent crime is committed by people who already have criminal histories.

Law-enforcement bureaucracies are like any other bureaucracy.

. . .

The Sayfullo Saipov case is another instance of serial institutional failure, from immigration authorities to domestic counterterrorism forces. We’ve given them tremendous amounts of money, manpower, and investigatory authority. Now we need to see results.